1. Field of the Invention
The present invention relates to a method for manufacturing an alloy wheel for an automobile, and more particularly to a method for manufacturing an automotive alloy wheel comprising a rim and a disc fitted in the rim.
2. Description of the Prior Art
In general, in manufacturing an alloy wheel for an automobile, it is desired to use aluminum or an aluminum alloy of high strength and light weight to afford a fine structure to the alloy wheel. In light of these objectives, it will be appreciated that a rim (or a drum) is a very important part in manufacturing an alloy wheel for an automobile.
The conventional methods for manufacturing a conventional alloy wheel can be classified into two types. The first being a liquid metal forging method of forging molten metal into a rim and disc complex, and the second being a continuous method of forging a disc type blank. However, the liquid forging method has disadvantages in that the method requires a complex liquid metal forging machine and a complicated process. It is also difficult to create a desired thickness of a rim for achieving an optimal strength and weight reduction. In addition, the continuous forging method has disadvantages in that a procedure for preparing a disc type blank material involves a large loss of raw material and a process for forging the disc type blank into a tube-shaped rim is considerably complicated.
In general, a forward and backward extrusion process is used for production of an alloy wheel rim from an aluminum tube. However, a large-sized pressing machine must be used to produce large tubes having an outer diameter of 400xcx9c700 mm and a thickness of 3.5xcx9c4.5 mm. Using this method, production costs are increased due to poor yield, thereby deteriorating economic efficiency. There is a process of forming a plate material by a deep drawing process, rather than the forward and backward extrusion process. However, this process is less economical because of the high price of aluminum plates and a large amount of loss when using plates. In addition to the above processes, there is a process of rolling a plate into a cylindrical form and subjecting the cylindrical form to an arc welding process. This process involves problems such as strength reduction of products owing to defects of weld zones, and air leakage from finally produced alloy wheels.
In a process for forming an aluminum tube according to a shape of a rim of an automotive alloy wheel, a spinning technique is predominantly used. The spinning technique is carried out in such a way that an aluminum tube is shaped by being worked with two or more small rollers passing over the tube while being rotated together with a mandrel. Therefore, the productivity rate of wheels depends on forward speed of rollers advancing along a full width of a rim while working the rim. Since the forward speed is determined by the deformation rate of a workpiece, the working speed usually becomes slow. Moreover, since movement of a roller must be controlled in a radial direction and a longitudinal direction of a tube, a control device is required and it is difficult to set the working condition of wheels.
Where a disc part is separately prepared and welded to a rim of an automotive alloy wheel, a TIG welding process or MIG welding process is usually employed for economic efficiency. The welding process involves the changing of dimensions of welded articles and the deterioration of working efficiency due to the high heat generated during the welding process. The welded articles may have defects after the welding process. Consequently, to apply the welding process to the production of an alloy wheel, additional weight is required for safety reasons. In addition, a correcting operation for the deformations of welded articles after a welding process is required. Hence, there is a need to improved the productivity and production cost of the manufacturing of alloy wheels.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art. An object of the present invention is to provide a method for manufacturing an alloy wheel for automobiles including a rim part having a portion running in and out from a rim flange to a drop center, and a disc part fitted in the rim part.
It is another object of the present invention to provide a method for manufacturing an alloy wheel for automobiles which is intended to remarkably reduce the number of process steps and simplify manufacturing instruments, thereby improving productivity and yield as compared with other methods.
It is still another object of the present invention to provide a method for manufacturing an alloy wheel for automobiles which is intended to produce a seamless tube having an optimal thickness and high strength and quality by a flowforming process.
It is a further object of the present invention to provide a method for manufacturing an alloy wheel for automobiles which allows a rim part to be subjected to a roll forming process at a high speed by rollers having a narrow range of control.
It is a further object of the present invention to provide a method for manufacturing an alloy wheel for automobiles which is designed to have welded a disc part to the rim part without a distortion of shape and necessity for a correction operation.
In order to accomplish the above object, the present invention provides a method for manufacturing an alloy wheel for automobiles, comprising the following steps: carrying out forging of an alloy billet to obtain a cup-shaped preform; carrying out flowforming of the preform to obtain a seamless tube; cutting the seamless tube into unit tubes; carrying out a primary roll forming of the unit tube to obtain a preliminarily shaped unit tube; carrying out a secondary roll forming of the preliminarily shaped unit tube to obtain a final shaped rim part; and attaching a disc part to the rim part.